The invention resides in a turbomolecular high vacuum pump with a circular intake area and in turbo-molecular pump groups formed by such pumps.
A turbo-molecular pump typically is of a rotational symmetrical design and includes typically the following sections: A compressor turbine, a pre-vacuum chamber and a drive module as well as a bearing unit. The compressor turbine includes chambers in each of which the same number of rotor and stator blade rings are arranged alternately closely adjacent to one another, wherein generally in each turbine chamber the blade or vane sets begin at the high vacuum end, that is the annular induction area, with a set of rotor blades. The rotor and stator blades or vanes are arranged inclined with respect to the direction of rotation and oriented oppositely so that during operation the gas particles are driven from the high vacuum toward the pre-vacuum area.
In vacuum processing turbo-molecular pumps are the most commonly used pumps for generating low pressures from ultra high vacuum to fine vacuum. Turbomolecular pumps with an annular induction area for the downstream turbine chamber may also be called single-flow passage turbo-molecular pumps. The drive arrangement and the main bearing structure are generally arranged in the pre-vacuum area, wherein, particularly the bearing unit—with a center of gravity-adjusted support of the rotor—extends into the interior of the rotor.
The active pumping area is the annular area at the induction opening as determined by the geometry of the turbine. There is always a pump-inactive, a so-called pumping-blind, circular area in the center. It is however particularly disadvantageous that, at the location of the turbomolecular pump itself, the recipient is not accessible for any purpose except the pumping. If a flange at the recipient is to be used for purposes other than pumping generally branched auxiliary structures such as T- or cross-pieces are mounted in between whereby the pumping effects directly at the recipient are drastically reduced (typically by at least 30%).
Because of the different circumferential speeds of the turbine blades at smaller and greater distances from the centers thereof (rinner and router) the pumping active annular area of the turbine is limited to certain radii ratios (rinner/router) which are known in the turbo-molecular pump technology.
For many applications, it would be advantageous if the central area around the turbine axis of a turbomolecular pump would be freely accessible also during operation, or if the recipient, extending at least partially around the turbomolecular pump, would be accessible in this area and/or if the pumping-active annular area could be differentially increased or a concentrically differential pumping would be possible.
With the description of what is impossible to achieve with the conventional turbomolecular pumps or what can be achieved only in a technically complicated way, the object of the invention is determined, that is to provide for the missing possibilities and to avoid technically complicated and disadvantageous designs.